Production of oxalic acid



United States Patent 3,081,345 PRODUCTION OF OXALIC ACID Emery J. Carlson, New Providence, and Everett E.

Gilbert, Morris Township, Morris County, N.J., assignors to Allied Chemical Corporation, New York, N.Y., a corporation of New York Filed Aug. 23, 1960, Ser. No. 51,456 7 Claims. (Cl. 2.60-533) The present invention relates to the production of oxalic acid. More specifically, the invention relates to the production of oxalic acid by oxidation of propylene.

Oxalic acid is conveniently obtained by oxidation of carbohydrates such as cane sugar, glucose, other sugars or mixtures thereof, starch, dextrin, etc. with nitric acid. An important disadvantage of this reaction, however, is that it is exceedingly ditficult to control, producing side reactions and; accordingly, resulting in-low yields.

It has beenproposed to produce oxalic" acid by the oxidation of propylene with-mixed acid. However, there are two objectionable features which preclude commercial acceptance of this procedure. One objection-is that propylene does not react rapidly with mixed acid of suitable strength. This not only imposes process and equipment limitations but introduces an element of hazard since unreacted propylene reacts with liberated nitrogen peroxide (N0 in the vapor space above the liquid level. Such mixtures of propylene and N0 can be violently explosive. A second objection is that recovery of spent sulfuric acid liquor, after filtration of the oxalic acid product, entails considerable evaporation because 'of the formation of large quantities of water.

It is an object of this invention to provide an efiicient and economical process for producing oxalic acid from propylene. A more specific object is to provide an eflicient and economical process for producing oxalic acid by two-step oxidation of propylene. Other objects and advantages of the invention will be apparent from the following description and examples.

In accordance with the broadest aspects of the invention, oxalic acid is produced by a two-step process in which (1) propylene is reacted with liquid N0 to form intermediate partial oxidation products, and (2) the partial oxidation products are then reacted at higher temperature with a member of the group consisting of mixed acid, nitric acid and liquid N0 to form oxalic acid as its dihydrate. The oxalic acid dihydrate may be puri- \fiCd by conventional recrystallization and Washing procedures and then converted into anhydrous oxalic acid by heating at temperature of about 95 to 100 C.

The first step of the present process is generally carried out within a temperature range of about -30 to 21 C., the preferred temperature ranging from about 15 to 10 C. Although use of temperature above 21 C. at

N0 boils at that point, higher temperatures may be employed at superatmospheric pressures. Generally speaking, at least about 1.5 and preferably at least about 3 mols of liquid N0 per mol of propylene are employed in this step. Particularly outstanding re-' sults have been obtained at ratio of about 4 to 5 mols of N0 per mol of propylene. v

The reaction of propylene with liquid N0 oxidizes the propylene to water-soluble intermediate partial oxidation products believed to be pyruvic or lactic acid or derivatives thereof. :In the second step of the process, these partial oxidation products are reacted at higher temperature with a member of the group consisting of mixed acid, nitric acid and liquid N0 to form the desired oxalic acid as its dihydrate. Optimum yields of oxalic acid are obtained by react .55 atmospheric pressure is not possible since pure liquid 3,081,345 Patented Mar. 12, 1963 ice ing the partial oxidation products with mixed acid (comprising nitric acid, sulfuric acid and water in varying proportions). Although somewhat lower yields are produced, nitric acid or liquid N0 may also be used as oxidizing agent.

When the oxidizing agent of the second step is mixed acid or nitric acid, reaction temperature ranging from about 60 to 120 C. is generally used, particularly out standing results having been obtained at temperature ranging from about 65 to C. In the case of liquid N0 the reaction temperature generally ranges from about 10 to 30 C. Although pure liquid N0 boils at 21 C., the presence of intermediate products or by-products, as well as impurities, in the reaction mixture enables use. of temperatures up to about 40 C. Higher reaction temperatures may be used in this step at superatmospheric pressures.

.When mixed acid is used as the oxidizing agent of the second step, the following broad and preferred mol ratios,

second step, ratios of about 3 to 5 mols, and preferably about 3.5 to 4.3 mols per mol of propylene are employed. Mol ratios equivalent to these ratios are employed when the oxidizing agent is liquid N0 The reaction of the partial oxidation products with mixed acid or nitric acid produces a gaseous effiuent rich in N0 This gaseous efiiuent may be condensed as crude N0 at sub-zero temperature and recycled to provide all or almost all of the N0 requirements of the first step of the process. Such condensation permits venting of the non-condensable CO CO, N 0 and N gases to the atmosphere. If the exit gases contain substantial quantities of N0 and NO that may have escaped condensation, the gases may be sent to a nitric acid recovery plant. If desired, the condensed crude N0 may be distilled before recycling. In this distillation, N 0 and NO impurities, together with a small amount of N0 are evolved and sent to the nitric acit' recovery plant. Liquid N0 is then taken off as the main cut and is recycled to the first step of the process. With such cyclic procedure, the only major raw materials required in the process are propylene and nitric acid, the latter in proportion to nitrogen values irrecoverably lost as N 0 and N and to recovery losses of NO and N0 Due to the rapidity of the reactions of this invention, the process can be operated continuously as well as batchwise.

In a modified embodiment of the process of the invention, the oxidation reaction may be carried out by addingpropylene to a mixture of liquid NO dissolved in mixed acid, followed by Warming to complete the oxidation. The first 'part of the reaction is generally carried out at temperature of about -30 to 21 C., preferably about .-15 to 10. C., and the reaction is completed at temperature of about 60. to C., preferably about 65 to 80 C.

reactor 2 via line 3 overa period of about /2 to 3 hours with stirring and cooling to maintain the temperature in the range of about 30 to 21 C. The mol ratio of N to propylene charge is at least about 1.5 to 1. A liquid effluent comprising intermediate partial oxidation products is formed in reactor 2.

Mixed acid, in ratio of about 3' to 5 mols of nitric acid, about 0.4 to 2.3 mols of sulfuric acid and about 4.6 to 25 mols of water per mol of propylene, is charged at temperature of about 60 to 120 C. through line 6 into reactor 5 provided with a stirrer and suitable cooling bath. The liquid effiuent from reactor 2 is then introduced into reactor 5 via line 4 over a period of about /2 to 3 hours with stirring and cooling to maintain the reactor contents at temperature of about 60 to 120 C. At the end of the period most of the reaction of the intermediate partial oxidation products and mixed acid has occurred. Alternatively, the liquid effluent from reactor 2 may be charged into reactor 5, and the mixed acid gradually added thereto while maintaining the reactor contents at the desired temperature of about 60 to 120 C. The resulting mixture is then held at temperature of about 60 to 120 C. for about /2 to 4 hours to complete the reaction.

A gaseous elfiuent rich in N0 is evolved during the reaction throughline 7 and passed to Dry-Ice condenser 8 where crude N0 is condensed while non-condensable gases, such as CO CO, N 0 and N are vented via line 9. The condensed crude N0 is then passed through line 11 to distillation still 12 where undesired N 0 and NO, together with a small amount of N0 are evolved through line 13 and sent to a nitric acid recovery plant. Liquid nitrogen peroxide is withdrawn as the main cut through line 14 and recycled to line 1 for introduction as charge to reactor 2.

The mixture in reactor 5 is passed through line 15 to crystallizer 16 where it is chilled, e.g. to temperature of about to -40 C., to crystallize out oxalic acid dihydrate. If desired or required, the ovalic acid dihydrate may then be purified in crystallizer 16 by conventional recrystallization and washing procedures using water introduced through line 17. The resulting slurry of oxalic acid dihydrate crystals is passed through line 18 to filter 19 where oxalic acid dihydrate is filtered ofi leaving a liquor consisting essentially of spent sulfuric acid. The spent sulfuric acid is withdrawn from filter 19 through line 21 and may be used in preparation of additional mixed acid. The oxalic acid dihydrate is passed through line 22 to dryer 23 where the dihydrate is dried to constant weight at temperature of about 40 to 75 C. The oxalic acid dihydrate is then withdrawn from the dryer through line 24 and may be readily converted to the anhydrous acid by heating at 95 to 100 C. for about 1 to 10 hours.

The following examples, in which parts are by weight, illustrate the invention.

EXAMPLE 1 Step 1.-97 parts of liquid N0 were placed in a reactor equipped with a stirrer and Dry-Ice bath, and 21 parts of propylene were introduced thereto over a 66 minute period at a uniform rate with stirring and cooling to temperature of --10 to 12 C.

Step 2.241 parts of mixed acid comprising 49% nitric acid, 29% sulfuric acid and 22% water were placed in a reactor of the type used in step 1 and heated to 70 C. The reaction mixture from step 1 held below 0 C. was added to the mixed acid over a period of 110 minutes in 5 to 10 ml. increments. The NO -rich gas evolved was condensed at Dry-Ice temperature, 108 parts of liquid N0 being collected. The mixture was then treated with 8 parts of additional mixed acid to complete the reaction, and the mixture was stirred for 60 minutes at 70 to 80 C. The mixture was chilled to 30 C. to crystallize oxalic acid dihydrate which was filtered and dried to constant weight at 40 to 50 C. The yield of oxalic acid dihydrate constituted 50.2 parts by theory).

Recycle.The first step was repeated using the liquid N0 recovered in the second step. The same quantity of propylene and N0 was used under the same conditions except that the reaction time was 58 minutes. The resulting mixture was then employed in repeating the second step using 255 parts of mixed acid and addition time of minutes. The yield of oxalic acid dihydrate was 51 parts (81% of theory). 117 parts of liquid N0 were collected for further recycling.

EXAMPLE 2 St p 1.-The procedure of Example 1 was repeated using 42 parts of propylene and 184 parts of liquid N0 with a reaction time of 128 minutes. After addition of the N0 the mixture was held for 60 minutes at -10 C. and then warmed to room temperature over a 90 minute period.

Step 2.-The mixture obtained in step 1 was added over a 70 minute period to 460 parts of mixed acid comprising 49% nitric acid, 29% sulfuric acid and 22% water at temperature of 66 to 82 C. The mixture was digested for 60 minutes at reaction temperature and then allowed to stand overnight at room temperature. After chilling, filtration and drying, 117 parts of oxalic acid dihydrate (yield-93% of theory) were obtained. Retreatment of the filtrate with 18 parts of mixed acid gave 3.5 parts of additional oxalic acid dihydrate for a total yield of 96% of theory.

EXAMPLE 3 Step I .-10 parts of propylene were reacted with 50 parts of liquid N0 in 22 minutes at 1 to 4 C. following the procedure set forth in Example 1.

Step 2.One-half of a mixture equivalent to that obtained in step 1 were mixed with 60 parts of mixed acid comprising 49% nitric acid, 29% sulfuric acid and 22% water. The mixture was heated to 70 C. at which point a violent exothermic reaction occurred, the temperature rising rapidly to 120 C. No cooling was applied, and the reaction was completed within 5 minutes. Chilling, filtration and drying of the mixture gave a yield of 8.1 parts of oxalic acid dihydrate (54% of theory).

When the second step was carried out under controlled conditions at 70 to 80 C., 10.9 parts of oxalic acid dihydrate were obtained (yield-73% of theory).

EXAMPLE 4 Step I.-10 parts of propylene were bubbled into 50 parts of liquid N0 contained in a cylinder immersed in an ice bath at reaction temperature of 0 C. over a 50 minute period.

Step 2.The mixture from step 1 was divided into two equal parts. One part was reacted with 77 parts of mixed acid in the manner set forth in Example 1 to produce 11.3 parts of oxalic acid dihydrate (yield-75% of theory). The second part was reacted with 54 parts of 70% nitric acid mixed with 0.5 part of concentrated sulfuric acid under the same reaction conditions. 7.3 parts of oxalic acid dihydrate were obtained (yield- 49% of theory). Heating of the filtrate gave an additional 0.5 part of oxalic acid dihydrate, raising the total yield to 52% of theory.

EXAMPLE 5 Step I.42 parts of propylene were reacted with 184 parts of liquid N0 over a period of minutes in the manner set forth in Example 1.

Step 2.One-half of the mixture obtained in step 1 was warmed to room temperature over a period of about 3% hours and then allowed to stand at room temperature for 5 days. 9 parts of oxalic acid dihydrate were filtered 0E. To the filtrate were added 28 parts of liquid N0 and the mixture was held at room temperature for 2 days. 12.5 parts of additional oxalic acid dihydrate were filtered off. This procedure was repeated twice more to give a total over 15 days of 33 parts of oxalic acid dihydrate (yield-52% of theory).

EXAMPLE 6 Step 1.4.2 parts of propylene were passed into a mixture of 51.5 parts of mixed acid (comprising 49% HNQ 29% H 50 and 22% H and 18.5 parts of liquid N0 contained in a cylinder provided with a Dry- Ice". l'ath over a 22 minute period at reaction temperatureof to C.

,Step 2.The mixture obtained in step 1 was slowly warmed to 55 C. The heat was removed, but the mixture spontaneously continued to warm to 70 C. in 10 minutes and finally to 100 C. in another 5 minutes. The mixture was held for one hour at 80 C. Chilling, filtration and drying gave 5.1 parts of oxalic acid dihydrate (yield-40% of theory). Retreatment of the filtrate with 5.1 parts of mixed acid gave 1.9 parts of additional oxalic acid dihydrate for a total yield of 56% offtheory.

All of the yields given in the above examples are crude yields. Upon recrystallization of these crude products from water, pure white oxalic acid dihydrate melting at about 102 C. may be obtained in at least about 80% yield.

Since certain changes may be made in carrying out this invention without departing from the scope thereof, it is intended that all matter contained in the above description shall be interpreted as illustrative and not in a limiting sense.

We claim:

1. A process for producing oxalic acid from propylene which comprises treating propylene with liquid nitrogen peroxide at temperature of about -30 to 21 C. to form intermediate partial oxidation products, and then heating the partial oxidation products with a member of the group consisting of mixed acid and nitric acid, said mixed acid constituting about 3 to 5 mols of nitric acid, about 0.4 to 2.3 mols of sulfuric acid and about 4.6 to 25 mols of waterper mol of propylene, at temperature of about 60 to 120 C. to form oxalic acid as its dihydrate.

2.' A process for producing oxalic acid from propylene which comprises treating propylene with liquid nitrogen peroxide at temperature of about 30 to 21 C. to form intermediate partial oxidation products, and then heating the. partial oxidation products with mixed acid constituting about 3 to 5 mols of nitric acid, about 0.4 to 2.3 mols of sulfuric acid and about 4.6 to 25 mols of water per mol of propylene at temperature of about 60 to 120 C. toform oxalic acid as its dihydrate.

3. A process for producing oxalic acid from propylene which comprises treating propylene with liquid nitrogen peroxide at temperature of about 30 to 21 C., in ratio of at least about 1.5 mols of nitrogen peroxide per mol of propylene, to form intermediate partial oxidation products, and then heating the partial oxidation products with a member of the group consisting of mixed acid and nitric acid, said mixed acid constituting about 3 to 5 mols of nitric acid, about 0.4 to 2.3 mols of sulfuric 5 which comprises treating propylene with liquid nitrogen peroxide at temperature of -30 to 21 C., in ratio of at least about 1.5 mols of nitrogen peroxide per mol of propylene, to form intermediate partial oxidation products, and then heating the partial oxidation products with mixed acid at temperature of about 60 to 120 C. to form oxalic acid as its dihydrate, said mixed acid constituting about 3 to 5 mols of nitric acid, about 0.4 to 2.3 mols of sulfuric acid and about 4.6 to 25 mols of water per mol of propylene.

5. A process for producing oxalic acid from propylene which comprises treating propylene with liquid nitrogen nitrogen peroxide at temperature of about to 10 ratio of at least about 3 mols of nitrogen peroxide per mol of propylene, to form intermediate partial oxidation prodnets, and then heating the partial oxidation products with mixed acid at temperature of about to C. to form oxalic acid as its dihydrate, said mixed acid constituting about 3.5 to 4.3 mols of nitric acid, about 1.3 to 1.6 mols of sulfuric acid and about 5.6 to 16.8 mols of water per mol of propylene. I

6. A cyclic process for producing oxalic acid from propylene which comprises treating propylene with liquid nitrogen peroxide at temperatures of about 15 to 10 C., in ratio of at least about 3 mols of nitrogen peroxide per mol of propylene, to form intermediate partial oxidation products, heating the partial oxidation products with mixed acid at temperature of about 65 to 80 C. to form oxalic acid as its dihydrate, said mixed acid constituting about 3.5 to 4.3 mols of nitric acid, about 1.3 to 1.6 mols of sulfuric acid and about 5.6 to 16.8 mols of water per mol of propylene, recovering gaseous nitrogen peroxide evolved during the reaction of the second step, liquefying said nitrogen peroxide by condensation and recycling the liquid nitrogen peroxide for reaction with propylene in the first step.

7. A'process for producing oxalic acid from propylene which comprises treating propylene, liquid nitrogen peroxide and mixed acid constituting about 3 to 5 mols of nitric acid, about 0.4 to 2.3 mols of sulfuric acid and about 4.6 to 25 mols of water per mol of propylene at temperature of about 30 to' 21 C. to form intermediate partial oxidation products, and then heating the partial oxidation products at temperature of about 60 to C. to form oxalic acid as its dihydrate.

References Cited in the file of this patent UNITED STATES PATENTS 2,847,464 Robertson et al Aug. 12, 1958 FOREIGN PATENTS 461,064 Canada Nov. 15, 1949 OTHER REFERENCES Beilstein: Organische Chemie, vol. II, page 503 (1920). 

1. A PROCESS FOR PRODUCING OXALIC ACID FROM PROPYLENE WHICH COMPRISES TREATING PROPYLENE WITH LIQUID NITROGEN PEROXIDE AT TEMEPRATURE OF ABOUT - 30* TO 21* C. TO FORM INTERMEDIATE PARTIAL OXIDATION PRODUCTS, AND THEN HEATING THE PARTIAL OXIDATION PRODUCTS WITH A MEMBER OF THE GROUP CONSISTING OF MIXED ACID AND NITRIC ACID, SAID MIXED ACID CONSTITUTING ABOUT 3 TO 5 MOLS OF NITRIC ACID, ABOUT 0.4 TO 2.3 MOLS OF SULFURIC ACID AND ABOUT 4.6 TO 25 MOLS OF WATER PER MOL OF PROPYLENE, AT TEMPERATURE OF ABOUT 60* TO 120* C. TO FORM OXALIC ACID AS ITS DIHYDRATE. 